Pressure vessels, such as, e.g., gas storage containers and hydraulic accumulators may be used to contain fluids under pressure. Some gas storage tanks are filled to a threshold pressure. The density of gases depends on the pressure and the temperature of the gas. For example, on a hot day, the gas will expand, and the tank may only fill to 75% (or less) of its potential. During refueling, the gas compresses into the tank and the temperature inside of the tank increases. As an example, in a high pressure system, the tank may be filled at a pressure of about 3,600 psi and an average temperature of about 50° C. (≈122° F.). After fueling, the temperature of the tank decreases (e.g., to the ambient temperature), and the pressure also decreases proportionally. In an example, the tank pressure decreases to 3,400 psi and this amounts to a thermodynamically induced underfill of about 6%.
According to ISO (International Organization for Standardization) 11439-Second Edition, a gas cylinder of Type 1 design is an all metal cylinder. A Type 2 design is a hoop wrapped cylinder with a load sharing metal liner and composite reinforcement on the cylindrical part only. A Type 3 design is a fully wrapped cylinder with a load sharing metal liner and composite reinforcement on both the cylindrical part and dome ends. A Type 4 design is a fully wrapped cylinder with a non-load sharing liner and composite reinforcement on both the cylindrical part and dome ends.